Microbiology-Lower GI Bacterial Infections Flashcards
Characteristics of enteric bacteria.
Gram negative rods, facultative aerobes.
Organisms that cause watery diarrhea w/ absence of PMNs
Secretory diarrhea is caused by
Organisms that cause diarrhea w/PMNs in stool, sometimes with blood and pus from damage to enterocytes.
Inflammatory diarrhea is caused by
Organisms that cause bloody diarrhea with or without inflammation
Hemorrhagic colitis is caused by
Organisms that cause systemic infections starting from the intestine
Enteric fever is caused by
Straight gram negative rods grown on MacConkey agar, glucose fermenters and oxidase negative.
Enterobacteriaceae
What enterobacteriaceae are not lactose fermenters?
Salmonella and shigella
How are bacteria serotyped?
O, H and K antigens expressed on their outer membrane.
What enterobacteriaceae are lactose fermenters?
E. coli, ETEC, EPEC, EHEC/STEC, EAEC
Most severe type of shigella, not as common in US
Shigella dysenteriae
Most common type of shigella in developing countries
Shigella flexnerii
Rarest type of shigella
Shigella boydii
Most common type of shigella in the US
Shigella sonnei
A patient presents to the clinic complaining of fever, abdominal pain, tenesmus (strain while defecating), low volume and bloody stools. Symptoms started a few days ago with watery diarrhea. Stool sample reveals fecal leukocytes with gram negative rods that do not ferment lactose on MacConkey’s agar and are non-motile. What is causing the patient’s symptoms?
Shigella presents this way because it release enterotoxin in the small intestine where it causes watery diarrhea. Once it reaches the large intestine you get dysentery.
Arthritis that can develop after Shigella infection
Reiter’s syndrome
Worst complication of Shigella infection
Shigella dysenteriae produces shiga toxin that can cause hemolytic uremic syndrome.
How does shigella infect the body?
They enter the gut through the M cells in the Peyer’s patches. After inducing apoptosis of the phagocyte, they infect the basolateral aspect of the enterocytes. Inside the enterocytes they replicate inside the cytoplasm which eventually lyses the enterocyte, allowing undergo cell to cell spread and evade the antibody response.
How does shigella move from cell to cell?
It hijacks the host cytoskeleton and propels itself with actin.
This is a normal colonic biopsy. What would a biopsy look like in a patient who had shigella?
3-7 mm colonic ulcer with lots of inflammatory cells.
What makes shigella so virulent?
It received a large virulence plasmid that allows it to spread from cell to cell. Also, virulence genes don’t turn on until about 37 degrees C.
What GI infections have humans as reservoirs?
Shigella, Typhoidal Salmonellae, ETEC, Vibrio
Why quarantine kids with shigella?
Can be transmitted very easily via feces, fingers, fomites and flies. Transmission is very efficient in crowds (POW camps, cruise ships, day care)
What GI infections have animals as reservoirs?
Non-typhoidal salmonellae, Yersinia, EHEC/STEC, Campylobacter jejuni (birds)
2 types of salmonella
Non-typhoidal salmonellae, typhoidal salmonellae
A patient presents with an abrupt onset of nausea, vomiting and diarrhea. Symptoms have persisted for 3 days. She has a low grade fever. Stool culture reveals a non-lactose fermenting, flagellated, motile and hydrogen sulfide gas producing gram negative rod. How do you treat this patient?
She has enterocolitis from infection by nontyphoidal salmonella. This bacteria is drug resistant so you do not prescribe antibiotics.
A patient presents with an abrupt onset of nausea, vomiting and diarrhea. Symptoms have persisted for 3 days. She has a low grade fever. Stool culture reveals a non-lactose fermenting, flagellated, motile and hydrogen sulfide gas producing gram negative rod. What would you worry about if this person was immunocompromised?
Sustained bacteremia from nontyphoidal salmonella. Patients will develop a septic temperature with few GI symptoms and a positive blood culture. Note that septic shock will happen very quickly because it is a gram negative organism with LPA.
A patient presents to the clinic with bloody diarrhea and a high-grade fever. Symptoms began about two weeks ago with constipation. Blood, urine and stool samples are positive for a non-lactose fermenting, flagellated, motile and hydrogen sulfide gas producing gram negative rod. What is causing these symptoms?
The patient has enteric fever (typhoid fever) from salmonella infection. Ingestion of contaminated food or water by a human causes small intestine colonization. Then it invaded Peyer’s patches via macrophages where it makes its home. Macrophages then travel around the body and cause systemic infection in the brain, lungs, bone, kidney, liver and gallbladder.
Travler’s diarrhea and children’s diarrhea?
ETEC enterotoxigenic E. coli. Causes malnutrition, stunted growth and low IQ in kids in the developing world.
How do you get infected with ETEC?
Ingestion of food contaminated w/human feces -> small intestine colonization by fimbriae stickage -> heat labile (LT) and heat stable (ST) enterotoxin production -> B subunit binds to cell -> A subunit enters and activates adenlylate cyclase -> constitutive activation of cAMP -> Cl- secreted w/reduced reabsorption -> massive fluid secretion into lumen of gut.
What type of E. coli causes the epithelial change shown below?
EIEC. It is identical to shigella a because it has the virulence plasmid that allows it to invade M cells, then enterocytes, then cause them to apoptosis and move to the next cell.
How does EPEC infect infants?
Has colonization fimbriae that allows initial binding to enterocyte. Late adherence forms pedestals and effaces villi, mediated by intimin.
A patient presents with abdominal pain, bloody diarrhea, and no fever. Stool sample reveals PMNs and a gram negative, lactose fermenting, oxidase negative rod. Blood sample reveals thrombocytopenia and microangiopathic hemolytic anemia. What is causing this patient’s symptoms?
EHEC and STEC can cause hemorrhagic colitis and hemolytic uremic syndrome. STEC and EHEC have a bacteriophage that allows them to produce shiva toxin. EHEC O157:H7 has an ability to produce attaching and effacing lesions (like EPEC) in addition to producing shiga toxin.
Why is shiga toxin so bad?
It is produced by bacteria in the intestine -> goes to kidneys -> binds Gb3 receptor on glomeruli -> inhibits protein synthesis -> destroys glomerular endothelium -> acute renal failure
A traveling 6 year old presents with inflammatory diarrhea with occasional blood and mucus. He progresses to hemolytic uremic syndrome. Tissue culture reveals stacked brick appearance. What is causing this condition?
EAggEC or EAEC. These have hydrophobic colonizing pili that cause dense bacterial aggregation. They also produce enterotoxins.
A patient has bloody diarrhea, cramps, vomiting and fever. His stool is positive for a gram-negative, tiny gull-shaped rods that are oxidase positive, this is the most common cause of diarrhea in the US. What is your diagnosis?
Campylobacter jejuni from undercooked meat (turkey, usually linked to birds)
A group of people present with profuse watery diarrhea “rice water stool”, vomiting, sunken eyes, poor skin turgor, and leg cramps. They are very dehydrated and electrolyte deficient. Stool sample reveals a gram negative, oxidase positive, glucose fermenting comma shaped rod. What is the most severe complication of this condition?
This is cholera. Cholera gravis is a result of hypovolemic shock due to massive amount of fluid loss.
A group of people present with profuse watery diarrhea “rice water stool”, vomiting, sunken eyes, poor skin turgor, and leg cramps. They are very dehydrated and electrolyte deficient. Stool sample reveals a gram negative, oxidase positive, glucose fermenting comma shaped rod. How does this microbe cause disease?
1) V. cholerae has colonization pili that adheres to small intestine 2) It makes cholera toxin: A subunit activates adenylyl cyclase via ADP ribosylation, B subunit binds to GM1 ganglioside molecules 3) Water and electrolytes flow out of cell.
